From jackrowe@compuserve.com Wed Aug 27 00:03:37 1997 Date: Tue, 26 Aug 1997 12:45:38 -0400 From: Jack Rowe To: PC List Subject: Legumes [The following text is in the "ISO-8859-1" character set] [Your display is set for the "US-ASCII" character set] [Some characters may be displayed incorrectly] Keith queried: >1. Are the non-native species of legumes that we use in >permaculture actually fixing much nitrogen, seeing very few of >us would be inoculating our seeds? Depends... some, as the medics, are great nitrogen-fixers and also great at finding the needed mycorhyzal (sp?) cohorts, at least here. Look to how the plants grow in depleted deep sandy soils for a hint as to whether they have found the bacteria. >2. At what point does the nitrogen fixed into nodules become >available? Do we have to wait for the plant to die? or are nodules >'sloughed off' during the life of the plant? Most of the nitrogen fixed by a legume -- from 40 to 90 percent or so -- ends up in the leaves (since leaf production is the major use of the nitrogen by the plant), so the tops are most important. Tops which are cut release from 40% (cut and let lie) to 60% (cut and dig in) of their nitrogen the first year, on average, and one might expect something analogous for the nitrogen in the roots. >3. Is there much point in planting legumes in rich soil >specifically for nitrogen fixing purposes? In accord with what you've written (nitrogen-fixing is suspended when soil nitrogen is adequate), no. Much more effective under conditions of high nitrogen is either 1) cropping, or 2) catch-cropping. Cropping is good sense, usually the soil is improved just for the purposes of cropping and receiving a yield. If season or other conditions are inappropriate, "catch crops" are used to capture nitrogen and any other available nutrients. For these purposes a catch crop is wanted that has high nutritional requirements for the mineral element in question. In the case of nitrogen, it's hard to beat the grasses -- annual rye, oats or wheat (crops), corn, etc. Dry matter production by grasses can easily double that of a good legume. I like the idea of a mix, such as of a grass and a leafy green such as mustard. On the other hand, the Land Institute in Kansas, USA has found in establishing prairie plant mixes that the more legume species that are included in an initial seeding, the greater will be the number of ALL species (whether legume, grass, broadleaf, etc.) which become established on a permanent basis. So nitrogen is not always the main or only issue. As for planting under trees, tap-rooted plants are best since fruit trees tend to concentrate feeder roots on or near the surface. Mustard is good here, too, comfrey, etc., but most grasses have phenomenal root systems and will compete strongly with fruit trees. Pasture mixes of non-competitive grass/legume mixes can be gotten from such supply houses as Peaceful Valley in California. Jack Rowe Cross Timbers Permaculture Institute Seeds of Texas Seed Exchange jackrowe@compuserve.com